Deflection yoke core for cathode ray tubes



Oct. 4, 1960 c. SNYDER DEFLECTION YOKE com FOR CATHODE RAY TUBES Filed June 19, 1957 United States Patent Oflice 2,955,220 Patented Oct. 4, 1960 DEFLE'CTION YOKE CORE FOR CATHODE RAY TUBES Christopher L. Snyder, Plainfield, N1, assignor to Steatite Research Corporation, Keasbey, N.J., a corporation of Delaware Filed June 19, 1957, Ser. No. 666,717

2 Claims. (Cl. 313-76) This invention relates to a ferromagnetic deflection yoke core for high efliciency deflection circuits for cathode ray tubes.

In cathode ray tubes a pair of horizontal and a pair of vertical coils are positioned on the outside thereof adjacent the neck portion of the tube for magnetically deflecting the electron beam of the tube. To improve the magnetic field applied, a yoke core of ferromagnetic material is positioned around the outside of the coils as a return circuit for the magnetic flux. Heretofore such magnetic coils have been employed to produce deflections of 7 to 90 but as cathode ray tubes are made shorter greater deflections of up to 110 are in use. To obtain greater deflections the coils and cores are extended beyond the actual neck portion of the tube and into the region surrounding the adjacent conic-a1 portion of the cathode ray tube. Thus the magnetic field is permitted to act on the beam of rays for a longer time deflecting the rays beyond the neck portion of the tube. Stronger magnetic fields or fields which are applied for a longer length of time to increase the deflections to over 90', however, introduce a certain amount of distortion into the resultant picture. This distortion corresponds to what is known as pin cushion distortion in optics.

Among the objects of the present invention is to provide a deflection yoke core for cathode ray tubes which nullifies the effect of pin cushion distortion.

Among other objects of the invention is to provide interfitting deflecting yoke core parts adapted to follow the contour of a cathode ray tube in the region where the neck joins the conical part and of reduced weight and to provide easily moldable contours.

These objects and others ancillary thereto are obtained by making the ferromagnetic core in several segments (four segments is customary) which when fitted together form a tube having an internal tube section of substantially uniform diameter which flares outwardly at one end almost to the edge of the outside diameter of the core to permit the segments to be fitted close to the flaring conical portion of the cathode ray tube. Each of the segments, however, has a flattened outer side such as may be obtained by symmetrically slicing a regular tubular segment longitudinally along a chord between the concentric inside and outside diameters thereof. Such slicing cuts through the flared portion of the interior opening. It has been found that distorting the core yoke in this way introduces a barrel effect into the images formed by the ray beams which can be ad justed to more or less nullify the fpin cushion eflfect due to the extension of the magnetic field. The barrel effect obtained by reducing the thickness of the intermediate portions of each of four segments and distorting the flared end of the core as described above may be made to exactly nullify the pin cushion effect but in many cases only an improvement or partial nullification of the pin cushion effect is required.

In the drawing:

Fig. 1 is an end view of an assembled yoke core made according to the invention.

Fig. 2 is an inside view taken on line 2-2 of one of the four similar parts of the yoke core of Fig. 1.

Fig. 3 is a partial view of a cathode ray tube partly in cross section illustrating how the yoke core of the invention is applied to a cathode ray tube.

Fig. 4 is a detail cross sectional view on an enlarged scale of the magnetic coil and yoke core on a cathode ray tube.

As is customary the yoke core 10 comprises four interfitting parts 11-14. Each of the four parts 11, 12, 13, 14 may be identical in shape and size as shown so that only one size of mold cavity is required for their manufacture. Only one such segment (11) need be described, therefore. The interfitting sides 21, 22 of the segments extend in a general radial direction and include projecting portion 23 on the inside of side 21, and projecting portion 24 on the outside of the other side portion 22. The interior segmental surface is generally tubular as at 25 but flares outwardly as shown at end 26.

In order to obtain any extensive flare in the end 26 it is necessary to make the segments relatively thick as shown by the dotted lines 27 in Fig. l. The pin-cushion elfect is nullified according to the present invention by slicing off the outside portion of the segment along the chord 28. This slice producm the curved edge 29 at the end 26 of the segment. It may be that the compensating barrelling efiect is due to the curved edge 29.

The yoke core segments 11-14 are held in position outside of the magnetic coils 3032 of cathode ray tube 40 by the clamp means 35 in the conventional manner. The dotted lines 41 of Fig. 3 show the possible path of cathode ray beams in the tube 40 and the angle illustrates how the deflection angle is measured.

The core segments may be made of any desired ferromagnetic material such as powdered iron, ferrous alloys and ferrites.

The features and principles underlying the invention described above in connection with specific exemplifications will suggest to those skilled in the art many other modifications thereof. It is accordingly desired that the appended claims shall not be limited to any specific feature or details thereof.

I claim:

1. A plural-segment tubular yoke core for cathode ray tubes, the assembled segments thereof forming an interior tubular opening of circular cross-sectional shape with said opening flaring outwardly at one end to the outer surface whereby the assembled segments may be fitted closely about the neck portion of a cathode ray tube in the region where said neck is joined to the conical portion of the tube while extending about a part of said conical portion of said tube, the outer portion of said assembled segments containing four symmetrically arranged, cutaway, flattened regions each forming with the internal flared opening a concave edge portion.

2. The yoke core as claimed in claim 1 wherein the assembled core is made up of tour substantially identical segments.

References Cited in the file of this patent UNITED STATES PATENTS 2,240,606 Bobb May 6, 1941 2,793,311 Thomas May 21, 1957 2,817,782 Over Dec. 24, 1957 OTHER REFERENCES Martin: Tele-Tech and Electronic Industries; December 1954, pages 82, 83, and 141. 

